Abstract: An apparatus for pumping an optical gain medium, such as a fiber gain medium, comprises a pump source having a plurality of different spatially separate or multiple wavelengths or wavelength bands which are all coupled into the fiber gain medium and provide at least one or more wavelengths to fall within the absorption band of fiber gain medium producing gain despite wavelength shifts in the pump source multiple wavelengths due to changes in the operating temperature of the pump source. At least one or more of the pump wavelengths will overlap the gain spectrum of the fiber gain medium sufficiently to continually provide high input power for pumping of the fiber gain medium.

Abstract: Two approaches are provided for achieving an optical amplifier system capable of producing high peak power, high energy pulse outputs while suppressing scattering noise. The first approach relates to an optical amplifier system which has at least one laser diode pulsed or cw pumped double clad fiber amplifier utilized for receiving a high frequency modulated injected signal pulse of short duration from the laser diode, via the fiber core, for amplification by coupling pump light into the inner cladding of the fiber. The average signal power is sufficient to saturate the gain of the fiber so as to minimize significant onset and buildup of forward and backward scattering noise. The duty cycle of the injected signal source pulse is chosen to allow adequate gain recovery in the fiber amplifier between pulses.